1. Field of the Invention
The present invention relates to an illuminating apparatus. More particularly, the present invention relates to an illuminating apparatus for obtaining a plane illumination having a high luminous intensity.
2. Description of the Related Art
A polycarbonate resin is defective in that, because of a transition absorption of electrons by the .pi.-.pi.* transition of the double bond in the benzene nucleus contained in the chemical structure, lights in the small-wavelength visible ray region (especially blue and green colors) are absorbed, the resultant light is tinged with yellow or orange, and the resin does not appear to be transparent, as shown in FIG. 1. In FIG. 1, the wavelength (nm) is plotted on the abscissa and the light transmission is plotted on the ordinate. The light transmission of polycarbonate is shown by curve 1.
To eliminate this defect, a method has been adopted in which a pigment having a maximum absorption to yellow or orange (generally called "a blueing agent") is incorporated to maximize the transmission of the wavelength corresponding to blue and produce a blueish tint. The light transmission of the blueing agent-incorporated polycarbonate is shown by curve 2 in FIG. 1.
However, the absorption at the left half portion of curve 2 is large and the resin is not transparent in the blue-to-red region, also the resin is practically useless from the viewpoint of an efficient transmission of the overall wavelength.